One of the most recognized multiple-access techniques for future communication systems is the non-orthogonal multiple access (NOMA). The basic idea behind NOMA is to serve multiple users on each orthogonal resource block. These resource blocks could be orthogonal bandwidths, different time steps, or orthogonal spacial directions in case the system contains multiple-antenna access points (AP). In the orthogonal multiple access (OMA) techniques, each resource block is dedicated to only one user, while in NOMA, multiple users are served on the same resource block. Thus, the spectral efficiency of the system is potentially improved by using NOMA by a factor of \(K\)  compared to OMA systems, \(K\)  being the number of users served on each orthogonal resource block.
Although it might seem that use of NOMA is always favorable, the application of NOMA is limited to the case where the direction of users' channel vectors are similar [1]}.
Therefore, to broaden the application of NOMA and to improve its performance, intelligent reflecting surfaces (IRS) can be utilized to manipulate the direction of the users' channel vectors [2]}.
